Facial development, with particular emphasis on the formation and morphology of the facial processes (medial and lateral nasal and maxillary processes) in normally and abnormally developing embryos is being analyzed. Examination of offspring of female mice treated with teratogenic levels of vitamin A and of mutant mice which spontaneously develop otocephaly indicates that although both the maxillary and mandibular processes are considered to form as part of the first visceral arch, these two processes develop quite differently. The source of, the migratory, biochemical and morphological characteristics of, and the teratogenic response of their constituent mesenchyme is being studied and compared. The relationship of abnormal maxillary process formation to cleft lip and cleft palate is also being analyzed.